Although IDA is a well-known risk factor for transfusion after TKA, and iron supplementation has been popularly used to optimize preoperative Hb levels before TKA22, it was found that anemia without iron deficiency, such as ACD or AOC, also accounts for 45% of preoperative anemia in patients undergoing TKA; thus, an appropriate correction method for ACD or AOC should also be considered for optimal preoperative optimization. Here, GSTM1 is linked to anemia (phenotype).